For a recording method by an ink jet printer, which is one typical method among a variety of color recording methods, a variety of ink discharge systems have been developed. These systems execute recording by generating ink droplets, which are adhered onto any of a variety of record-receiving materials (e.g., paper, film, and fabric, etc.). According to this method, a recording head is not brought into direct contact with the record-receiving material; therefore, generation of noise can be avoided thus achieving silent recording. In addition, due to having the feature of reduced size, increased speed and coloring being readily achievable, prevalence in recent years has been in rapid progress, and thus great advancement hereafter is expected.
Inks containing a water-soluble coloring matter (dye) dissolved in an aqueous medium have been used as conventional inks for fountain pens, felt pens etc., and inks for ink jet recording. To these inks is generally added a water-soluble organic solvent in order to prevent pen tips or ink discharge nozzles from clogging with the ink. For these inks, demanded are performances such as ability to generate a recorded image with satisfactory density, probability of avoiding occurrence of clogging at the pen tips and nozzles, favorable drying characteristics on the record-receiving materials, suppression of bleeding, superior storage stability, and the like.
Clogging of nozzles of ink jet systems often results from hardening and deposition of a coloring matter when the moisture of the ink evaporates faster than other solvent and additives in the vicinity of the nozzle to cause a state of the composition including less moisture and a substantive amount of the solvent and additives. Therefore, one extremely important expected performance is that solids are less likely to be deposited even in the state in which the ink contains a low amount of moisture. On this ground, high solubility in the solvent and additives is also a property required for coloring matters. Also, in a known procedure for resolving a problem of clogging of nozzles, a coloring matter capable of providing a high print density is used. By using a coloring matter having a high print density, the content of the coloring matter in an ink can be reduced while maintaining a print density according to conventional procedures. This not only results in reduction of probability of deposition of the coloring matter, but also is advantageous in terms of costs, and thus development of a coloring matter having higher print density has been desired.
In the meantime, for recording image or character information on a color display of computers in full color by an ink jet printer, subtractive color mixing with four inks having different colors of, generally yellow (Y), magenta (M), cyan (C), and black (K) has been employed, whereby the recorded image is presented in full color. In order to reproduce an additive color mixing image formed with red (R), green (G), blue (B) on a CRT (cathode ray tube) display and the like as strictly as possible using subtractive color mixing, it is desired that Y, M and C, among the coloring matters used in inks, have a hue approximate to the standard color, and are brilliant, respectively. The term brilliance as herein referred to means, in general, to have a high chroma saturation. When three primary colors of Y, M and C having a low chroma saturation are used, narrowing occurs of the color region that can be expressed by a simple color or a mixed color, whereby the range of the color region to be expressed may be insufficient. Therefore, development of a coloring matter having a high chroma saturation, and an ink containing the same have been desired.
In addition, long term storage stability, as well as high density of the recorded image, and superior fastness such as water resistance, moisture resistance, light resistance and gas resistance of the image are also required properties for the inks. Herein, gas resistance means resistance to a phenomenon of causing discoloration and fading of a recorded image via a reaction of a gas present in the air and having an oxidizing action, with a coloring matter (dye) of the recorded image on or in the record-receiving material. Particularly, ozone gas among oxidizing gasses is considered as a main causative substance that promotes the discoloration and fading phenomenon of ink jet recorded image. Since this discoloration and fading phenomenon is characteristic in ink jet recorded images, improvement of the ozone gas resistance is a significant technical problem in the art.
Advancement of ink jet techniques in recent years has lead to a considerable increase in the speed of ink jet recording (printing). Thus, similarly to laser printers using an electronic toner, use of ink jet printers has started for printing of documents on plain paper which has a main application in office environments. Prevalence of the ink jet printers has been in progress particularly in small to medium scale office environments such as SOHO in particular, due to advantages such as no limitation of usable recording paper, and low cost of the printer itself. When an ink jet printer is thus used for applications in printing on plain paper, hue, color formation (printing) density and water resistance tend to be regarded more importantly among qualities required for printed matter.
For the purpose of achieving these performances, a method in which a pigment ink is used was proposed. However, pigment inks do not have a state of solution as the coloring matter is not dissolved in an aqueous ink, but have a state of dispersion. Therefore, use of a pigment ink in ink jet recording may involve problems of stability of the ink per se, problems of clogging of nozzles of recording heads, and the like. In addition, when a pigment ink is used, a problem in connection with abrasion resistance often occurs. In the case of the dye inks, the aforementioned problems are reported to be comparatively less likely to occur; however, dye inks are significantly inferior particularly in water resistance as compared with pigment inks, and improvement of this disadvantage has been strongly desired. In addition, unlike pigment inks, dye inks are likely to involve problems of lowered coloring density as a result of faster permeation of the coloring matter adhered onto the surface of a plain paper by ink jet recording toward the back face direction of the paper.
In one method for attaining ink jet recorded images of photo image qualities, an ink receiving layer may be provided on the surface of a record-receiving material. In an ink receiving layer which is provided for such a purpose, a porous white inorganic substance is often included for facilitating drying of the ink and for minimizing bleeding of the coloring matter to provide high quality images. However, discoloration and fading due to ozone gas is markedly observed particularly on such a record-receiving material. Along with recent prevalence of digital cameras and color printers, the opportunity for printing images with photo image quality obtained by a digital camera or the like have increased also at home. Thus, discoloration and fading of the recorded image due to the oxidizing gas as described above has been a concern. With regard to yellow coloring matters, those having favorable resistance against oxidizing gas as well as light resistance have been proposed, as compared with others among three primary colors, i.e., magenta and cyan. However, yellow coloring matters for ink jet recording and yellow inks having high brilliance required for market, and also having various types of fastness properties that are sufficiently satisfactory have not yet been obtained.
As a well-known yellow coloring matter for ink jet that is superior in water solubility and brilliance, C. I. (Color Index) Direct Yellow 132 is exemplified. Furthermore, a plurality of azo yellow coloring matters having superior fastness properties have been proposed on the basis of development of yellow coloring matters for ink jet recording in recent years.    Patent Document 1 discloses an anionic azo yellow compound having light resistant and water resistant fastness.    Patent Document 2 discloses a water-soluble yellow azo compound having high solubility in water, moisture resistance, ozone gas resistance, and light resistance.    Patent Document 1: Japanese Unexamined Patent Application, Publication No. H4-233975    Patent Document 2: Japanese Unexamined Patent Application, Publication No. 2006-152264